In general, a computer tomography apparatus (CT) for medical purposes has a construction shown in FIG. 1. The best feature of the CT for medical purpose is a circular ring called as a gantry 15. In the frame of the ring thereof, the CT beam transmission part 10 and the X-ray detector 20 are opposed to each other.
At this time, in the X-ray detector 20, the X-ray detecting elements are linearly arranged. The CT beam transmission part 10 transmits the X-ray of a fan beam shape toward only the linear elements of the X-ray detector 20.
In order to do a computed tomography scan on a subject (patient), it is necessary to scan the subject at an angle of 360 degrees. As shown in FIG. 2 and FIG. 3, the CT beam transmission part 10 and the X-ray detector 20 are moved left and right to be scanned. Or, As shown in FIG. 4 and FIG. 5, the CT beam transmission part 10 and the X-ray detector 20 are rotated to be scanned.
Meanwhile, in the computer tomography apparatus (CT) for medical purposes using another method, it rotates the gantry, so that the subject (patient) can be continually scanned.
Also, it is necessary to longitudinally scan the subject (patient) at an angle of 360 degrees. In order to solve this demand, the bed, on which the patient is lying, is horizontally moved parallel to the rotation axis thereof in the inside of the gantry, which is under a continuous rotation scanning.
The scanning methods are already well-known in the prior art. In these scanning methods, the X-ray detecting elements are linearly arranged on the detector and the X-ray of the fan beam shape is irradiated. At this time, it scans the patient in the direction of the axis of ordinates, so that the radiation exposure on the patient can be minimized.
In the meantime, in order to prevent the scan result from being deteriorated owing to the unconscious movement of the patient during the scanning, it is necessary to scan the patient as soon as possible.
In this case, it is necessary to rotate the gantry having a significant weight as soon as possible and minimize the irregular vibration of the gantry. Accordingly, the cost of constructing the hardware for satisfying these requirements is considerable.
In the meantime, the industrial computer tomography apparatus does not need parts of the technical requirements, which is required in the medical computer tomography apparatus.
That is, in case of inanimate subjects, there is no need to minimize the radiation exposure and complete the scan in the least amount of time. That is, it is not necessary to rotate the CT beam transmission part and the X-ray detector to high speeds through the gantry like the medical CT. In some cases, the CT beam transmission part and the X-ray detector are rather fixed and the subject is rotated at an angle of 360 to be scanned.
Like this, the gantry or the subject are rotated to low speeds, so that the irregular vibration can be decreased, thereby more improving the resolution of the computer tomography.
That is, the industrial CT can obtain a better result thereof at a low cost in comparison with the medical CT.
In industry, since the articles of requiring the X-ray CT are very various, the industrial X-ray CT is often customized in consideration of the characteristic of the subject. Mainly, the formats of each part thereof are divided into several kinds in consideration of the shape and size of the subject.
Firstly, in the most common manner, the CT beam transmission part and the X-ray detector are fixed to both ends thereof and the rotation axis is linearly arranged between them. At this time, the subject located on the rotation axis is rotated at an angle of 360 degrees to be scanned.
Large numbers of the computer tomography apparatuses for scanning the general industrial products such as a tire or an electronic substrate belong to this shape.
In some cases, the rotation axis located between the CT beam transmission part and the X-ray detector can be manufactured in the variable type so as to be moved along any one of three linear axes.
For special example, in the dental CT, the CT beam transmission part and the X-ray detector include a pair of gantries, so that they rotate the surroundings of the head of the patient at an angle of 360 degrees to be scanned.
In case of the general CT for medical purpose, since it rotates the surroundings of the head of the patient sitting, the rotation axis is located on the upper part of the patient's head and it horizontally rotates the surroundings of the head of the patient.
That is, the gantries of the general medical CT and the dental CT form an angle of 45 degrees. However, the rotation directions thereof are different from each other.
In rare cases, the subject is fixed thereto or horizontally moved and the gantry rotates the surroundings of the subject.
In this case, as described above, the resolution thereof can be deteriorated owing to the vibration phenomenon of the gantry.
In the field of the geological resource, the X-ray scan is typically conducted so as to grasp the physical properties of the drilling core obtained by the stratum drilling.
Since the shape of the drilling core is a cylinder, where the X-ray scan is simply performed with the object of viewing the interior structure thereof, it is not easy to grasp the physical properties inside the core owing to very different X-ray transmission images between the middle and edge portions thereof.
In order to overcome the problem in the field of the geological resource, a thin slab (piece type) sample is again collected from the geological sample to be X-ray scanned.
However, in case of collecting the sample in addition, it is time-consuming. Also, in case of any core sample obtained from soft stratum, it is not easy to collect the piece type sample itself.
In order to solve this problem, the research organization of the geological resource all over the world had been tried to scan the core itself through the computer tomography apparatus. However, the optimization CT on the sample core of the cylinder shape is not yet developed. That is, it remains an unsolved problem.
In other word, since the cylinder type sample has a very long major axis, it cannot smoothly perform the experiment required in the field of the geological resource by using the CT beam transmission part and the X-ray detector and by means of the arranging and operating manners of the rotation axis used in the existed industrial CT.
In order to solve this problem, it has been tried to scan the core itself through the medical computer tomography apparatus. However, the core sample requires more sufficient X-ray san than that of the medical CT. Accordingly, it cannot also, smoothly perform the experiment required in the field of the geological resource.
Meanwhile, in the field of the geological resource, a very small fragment or a very small mini core of a cylinder shape are again collected from the core sample to be CT-scanned.
At this time, in order to observe the minute physical properties of the core such as a microcrack or a particle array pattern etc. under high resolution, it often utilizes the method of the geometric magnification.
Generally, since the size of the detector is limited, where the size of the subject is small, it is easier to geometrically magnify the subject.
In order to focus the maximum image inside the detector, it is necessary to perform the CT scan with the rotation axis near the CT beam transmission part as possible.
When it treats the considerable small samples, since the CT beam can sufficiently penetrate the samples by means of only a small X-ray power, the CT beam transmission part having a small voltage capacity and a high resolution is utilized. Accordingly, in accordance with this structure, there is a general trend of manufacturing and using the micro X-ray CT separately.
The CT apparatuses generate the radiation without exception. Accordingly, to shield the X-ray properly is a main task for the CT fabrication.
In case of the medical CT, as described above, it is constructed in such a manner that the radiation exposure of the patient can be minimized and then, the radiation is emitted on the patient without separate shielding. In the meantime, in order to shield the radiation on the workers of the CT control room etc., the outside of the scanning room is shielded from the radiation, so that it can prevent the radiation from penetrating the CT control room etc.
However, In case of the industrial CT, since it has any voltage much higher than the medical CT and emits the radiation longer than the medical CT, the sufficient shielding device should be prepared at any cost.
In the most common shielding manner, it constructs a cabinet type shielding device, so that the entire CT including the CT beam transmission part, the X-ray detector and the rotation axis between them is surrounded by a lead plate etc. to be shielded.
That is, the CT includes the shielding device located on the outside thereof.
However, in this case, since the entire space thereof is restricted by the size of the cabinet, the size of the analyzing sample is restricted without question.
Accordingly, it is necessary to suggest an alternative, instead of the cabinet type shielding device. Also, it seeks to properly control the surrounding conditions such as a temperature and a humidity etc. suitable for the condition of the experimental sample.
Recently, in the field of the geological resource, it spurs the exploration and development of the special sample called as a gas hydrate, thereby the demand on the CT scan has been remarkably increased.
The gas hydrate is spread in the deep seafloor or subsurface thereof. The hydrate is existed in the form of an ice owing to the low-temperature and high-pressure condition provided by the surroundings thereof. Also, it contains much marsh gas therein.
Since the gas hydrate is dissociated in a state of nature to be dissipated, the sample should be stored in an extremely low temperature or pressure vessel having a hard pressure so as to protect it in good condition. At this time, the latter is widely used, because it is closer to the state of nature.
The gas hydrate is collected together with the stratum drilling. Accordingly, the cylinder type core, that is, the core sample is composed of the gas hydrate along with the perimetrical sediment.
Accordingly, the container of filling the gas hydrate is a cylinder type and made of a metal component capable of handling the pressure well.
Since it cannot take out and observe the sample from the opaque container, the CT scan manner is experimentally applied thereto. The material of the container is an X-ray permeable metal such as an aluminum.
Also, as though the gas hydrate is contained in the metal container, where the gas hydrate is completely dissociated, it can explode. Moreover, it keeps the gas hydrate pressure refrigerated in a temperature of 4° all the time.
That is, in the CT experiment on the gas hydrate sample, to maintain the temperature condition of about 4° around the CT apparatus is the key to success. However, it is very difficult for the existed cabinet type shielding CT to meet this condition.
If a refrigerator is installed in the inside of the small cabinet type shielding membrane, since the vibration generated by the operation of the refrigerator is directly transmitted to the CT parts, it is hard to obtain the high resolution material.
Accordingly, where the gas hydrate sample is presently scanned through the CT apparatus in the field of the geological resource, the research teams all over the world have been searched for the optimum plan as to whether the special facility for controlling the temperature and humidity around the CT is combined with the CT apparatus or not.
Also, a big cylinder capable of covering the subject is required. Moreover, it is necessary to make any device capable of rotating the CT beam transmission part and the detector or moving them left and right at the same time. Accordingly, the manufacturing cost thereof becomes more expensive. Since the CT beam transmission part and the detector are rotated or moved left and right, it is frequently out of work, thereby increasing the maintenance cost. Also, since the operations of rotating or horizontally moving the CT beam transmitter and the detector are large, it is out of focus, thereby it has difficulty in performing the accurate measurement.
Accordingly, it has considerable difficulty for using as the industrial CT, besides the medical CT. An improvement thereof has been remained a big issue in the art.